Recording fluid for the ink jet process

ABSTRACT

A recording fluid for the ink jet process contains a water-miscible organic solvent and a dye of the formula ##STR1## where R 1 , R 2 , R 3  and R 4  each have specified meanings, An⊖ is an anion and X is a bridge member of the formula ##STR2## where Y and the rings A and B each have specified meanings.

The present invention relates to a novel recording fluid for the ink jet process, containing a water-miscible organic solvent and a basic dye which has two 6-hydroxypyrid-2-one radicals which each carry a pyridinium radical in ring position 5 and are linked in ring position 3, in each case via an azo group, by means of a bridge member from the diaryl(hetero)alkane, arylazoaryl, arylcarbonylaminoaryl or arylsulfonylaminoaryl series.

The ink jet process is known per se. In this process, droplets of a writing fluid are directed from one or more small nozzles at a substrate, for example paper, wood, textiles, plastic material or metal, in an electronically controlled manner whereby the individual droplets are organized into characters or graphic patterns.

Recording fluids suitable for the ink jet process generally contain dyes which are soluble in water and/or organic solvents as colorants. However, some of these dyes have deficient application properties, for example poor water fastness or smudge resistance.

It is an object of the present invention to provide a novel ink jet process recording fluid in which the dyes present therein should have a favorable range of application properties.

We have found that this object is achieved with a novel recording fluid for the ink jet process, containing a dye and a water-miscible organic solvent, wherein the dye is a dye of the formula I ##STR3## where

An.sup.⊖ is an anion,

R¹ and R³ are identical or different and each is independently of the other hydrogen, C₁ -C₄ -alkyl, carboxyl, C₁ -C₄ -alkoxycarbonyl, carbamoyl or C₁ -C₄ -monoalkyl- or -dialkyl-carbamoyl,

R² and R⁴ are identical or different and each is independently of the other hydrogen or C₁ -C₄ -alkyl which may be substituted by amino, C₁ -C₄ -monoalkyl- or -dialkyl-amino or by the radical ##STR4## where R⁵, R⁶ and R⁷ are identical or different and each is independently of the others C₁ -C₄ -alkyl and An.sup.⊖ has the abovementioned meaning, and

X is a bridge member of the formula II or III ##STR5## where Y is C₁ -C₆ -alkylene which may be interrupted by oxygen, imino or C₁ -C₄ -alkylimino, or is --N═N--, --CO--NH-- or --SO₂ --NH--, and the rings A and/or B may each be benzofused and/or substituted by C₁ -C₄ -alkyl, hydroxyl, C₁ -C₄ -alkoxy, amino, C₁ -C₄ -monoalkyl- or -dialkyl-amino or hydroxysulfonyl.

All the alkyl and alkylene radicals appearing in the abovementioned formulae may be not only straightchain but also branched.

Anions An.sup.⊖ are derived from inorganic or organic acids and are for example fluoride, chloride, bromide, hydrogensulfate, sulfate, aminosulfate, methosulfate, ethosulfate, perchlorate, tetrafluoroborate, trichlorozincate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, formate, acetate, propionate, lactate, benzoate, oxalate or succinate.

The radicals R¹, R², R³, R⁴, R⁵, R⁶ and R⁷ are each for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl or sec-butyl.

Radicals R¹ and R³ are each further for example methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, isobutoxycarbonyl, secbutoxycarbonyl, mono- or dimethylcarbamoyl, mono- or diethylcarbamoyl, mono- or dipropylcarbamoyl, mono- or diisopropylcarbamoyl, mono- or dibutylcarbamoyl or N-methyl-N-ethylcarbamoyl.

Radicals R² and R⁴ are each further for example 2-aminoethyl, 2-methylaminoethyl, 2-dimethylaminoethyl, 2- or 3-aminopropyl, 2- or 3-methylaminopropyl, 2- or 3-dimethylaminopropyl, 2- or 4-aminobutyl, 2- or 4-methylaminobutyl or 2- or 4-dimethylaminobutyl.

Radicals R² and R⁴ are each further for example ##STR6##

Y is for example methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, 1-methylethylene, 1,2-dimethylethylene, 2-methyltrimethylene, 2-oxatrimethylene, 2-azatrimethylene, 2-aza-2-methyltrimethylene, 3-oxapentamethylene, 3-azapentamethylene or 3-aza-3-methylpentamethylene.

Preference is given to a recording fluid which contains those dyes of the formula I where

R¹ and R³ are each hydrogen, methyl or ethyl,

R² and R⁴ are each hydrogen, dimethylaminopropyl or diethylaminopropyl and

X is a bridge member of the formula IIa or IIIa ##STR7## where Y is C₂ -C₄ -alkylene, in particular ethylene, --CO--NH-- or --SO₂ --NH--.

The dyes of the formula I are mostly known and described for example in DE-A-2,627,680, DE-A-3,302,614 or DE-A-3,213,826 or can be obtained by the methods recited therein (loc. cit.).

The novel recording fluid for the ink jet process contains one or more dyes of the formula I and a water-miscible organic solvent.

Water-miscible organic solvents are for example C₁ -C₄ -alkanols, such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol or tertbutanol, carboxamides, such as N,N-dimethylformamide or N,N-dimethylacetamide, lactams, such as N-methylpyrrolid-2-one, cyclic ureas, such as 1,3-dimethylimidazolidin-2-one, ketones or ketoalcohols, such as acetone, methyl ethyl ketone or 2-methyl-2-hydroxypentan-4-one, ethers, such as tetrahydrofuran or dioxane, mono-, oligo- or polyalkylene glycols or thioglycols with C₂ -C₆ -alkylene units, such as ethylene glycol, 1,2- or 1,3-propylene glycol, 1,2- or 1,4-butylene glycol, 1,6-hexylene glycol, diethylene glycol, triethylene glycol, thiodiglycol, polyethylene glycol or polypropylene glycol, other polyols, such as glycerol or hexane-1,2,6-triol, C₁ -C₄ -alkyl ethers of polyhydric alcohols, such as ethylene glycol monomethyl or monoethyl ether, diethylene glycol monomethyl or monoethyl ether or triethylene glycol monomethyl or monoethyl ether, or dimethyl sulfoxide.

Water-miscible organic solvents which are preferred are for example N-methylpyrrolidin-2-one, mono-, di- or trialkylene glycols with C₂ -C₆ -alkylene units, in particular mono-, di- or triethylene glycol, or dimethyl sulfoxide. Very particular preference is given to N-methylpyrrolidin-2-one, diethylene glycol and dimethyl sulfoxide.

The proportion of dye of the formula I is in general from 2 to 10% by weight, preferably from 3 to 5% by weight, each based on the total weight of the recording fluid.

Preference is given to a recording fluid which, besides the dye of the formula I and a water-miscible organic solvent, additionally contains water.

In this case, the novel recording fluid for the ink jet process contains in general from 50 to 95% by weight, in particular from 70 to 95% by weight, each based on the total weight of the solvent system, of water.

The novel recording fluid may also contain assistants, for example agents for affecting the viscosity, such as polyvinyl chloride or cellulose derivatives, surfactants (nonionic, anionic or cationic) or buffer systems.

The following examples will explain the invention in more detail:

General method for preparing a recording fluid

From 4 to 5 parts by weight of a dye which has been freed from electrolytes by the conventional method of reverse osmosis are dissolved in from 95 to 96 parts by weight of a liquid whose composition is given in the examples below. The solution is pressure filtered through a Teflon filter of pore size 1 μm and then devolatilized under reduced pressure.

This recording fluid is charged to the receiving vessel of an ink jet printing head which expels the ink in droplet form under the action of supplied heat. This thermal ink jet printing head is used to print a commercial type of paper as used for typescript.

The smudge resistance of the script obtained is tested by two methods:

Method 1: marking the scripts with a commercial text marker

Method 2: rubbing a written area with a moistened finger

The fastness of the script is assessed on a scale from 5 to 1, where 5 denotes the absence of bleeding and 1 denotes that the script has become so smudged that it is no longer legible.

The inks were prepared using the dyes of the formula ##STR8## described in Table 1.

                                      TABLE 1                                      __________________________________________________________________________     Dye                                                                            No.                                                                               R.sup.1                                                                            R.sup.2                                                                               R.sup.3                                                                            R.sup.4                                                                               X                      An.sup.⊖               __________________________________________________________________________     1  H   H      H   H                                                                                      ##STR9##              chloride                       2  3-CH.sub.3                                                                         H      3-CH.sub.3                                                                         H                                                                                      ##STR10##             chloride                       3  H   CH.sub.3                                                                              H   CH.sub.3                                                                               ##STR11##             chloride                       4  H   H      H   H                                                                                      ##STR12##             chloride                       5  3-CH.sub.3                                                                         H      3-CH.sub.3                                                                         H                                                                                      ##STR13##             chloride                       6  H   CH.sub.3                                                                              H   CH.sub.3                                                                               ##STR14##             chloride                       7  H   C.sub.3 H.sub.6 N(CH.sub.3).sub.2                                                     H   C.sub. 3 H.sub.6 N(CH.sub.3).sub.2                                                     ##STR15##             chloride                       8  H   C.sub.3 H.sub.6 N(CH.sub.3).sub.2                                                     H   C.sub.3 H.sub.6 N(CH.sub.3).sub.2                                                      ##STR16##             chloride                       9  H   C.sub.3 H.sub.6 N(CH.sub.3).sub.2                                                     H   H                                                                                      ##STR17##             chloride                       10 H   H      H   H                                                                                      ##STR18##             chloride                       __________________________________________________________________________

Dyes 1, 2, 3, 4, 5 and 6 were prepared as described in Examples 1, 50, 55, 7, 61 and 66 of DE-A-2,627,680, dyes 7, 8 and 9 as described in Examples 33, 34 and 35a of DE-A-3,302,614 and dye 10 as described in Example 49 of DE-A-3,213,826.

The composition of the inks and the smudge resistance ratings of the script are reported in Table 2. The water-miscible solvents (diethylene glycol or a mixture of diethylene glycol and N-methylpyrrolidin-2-one) are abbreviated to DEG and NMP. W denotes water.

                                      TABLE 2                                      __________________________________________________________________________     Applica-                                                                               Proportion of dye                                                      tion    in recording                                                                            Composition of Fastness by                                    Example                                                                             Dye                                                                               fluid    solvent system Method                                                                              Method                                    No.  No.                                                                               [% by weight]                                                                           [parts by weight]                                                                         Color                                                                              1    2                                         __________________________________________________________________________     1    1  4.5      W:DEG = 9:1                                                                               yellow                                                                             5    4-5                                       2    2  4.5      W:DEG = 9:1                                                                               yellow                                                                             4    4                                         3    3  4.5      W:DEG = 9.5:0.5                                                                           yellow                                                                             4-5  4                                         4    4  4.0      W:DEG = 9:1                                                                               orange                                                                             4    4-5                                       5    5  4.0      W:DEG = 9:1                                                                               orange                                                                             4    3-4                                       6    6  4.5      W:DEG = 9:1                                                                               orange                                                                             4    4                                         7    7  5        W:DEG:NMP = 6:3:1                                                                         black                                                                              5    4-5                                       8    8  5        W:DEG:NMP = 6:3:1                                                                         black                                                                              4-5  4-5                                       9    9  4.5      W:DEG:NMP = 6:3:1                                                                         black                                                                              4-5  4                                         10   10 4.5      W:DEG:NMP = 6:3:1                                                                         black                                                                              4    3-4                                       __________________________________________________________________________ 

We claim:
 1. An ink jet process which comprises applying a recording fluid consisting essentially of 2-10% by weight of a dye, a water-miscible organic solvent, and 70 to 95% by weight of water, wherein the dye is represented by the formula I ##STR19## where An⁻ is an anion,R¹ and R³ are identical or different and each is independently of the other hydrogen, C₁ -C₄ -alkyl, carboxyl, C₁ -C₄ -akloxycarbonyl, carbamoyl or C₁ -C₄ -monoalkyl- or dialkyl-carbamoyl, R² and R⁴ are identical or different and each is independently of the other hydrogen or C₁ -C₄ -alkyl which may be substituted by amino, C₁ -C₄ -monalkyl- or dialkyl-amino or by the radical ##STR20## where R⁵, R⁶ and R⁷ are identical or different and each is independently of the others C₁ -C₄ -alkyl and An⁻ has the above-mentioned meaning, and X is a bridge member of the formula II or III ##STR21## where Y is C₁ -C₆ -alkylene which may be interrupted by oxygen, imino or C₁ -C₄ -alkyamino, or is --N═N--, --CO--NH-- or --SO₂ --NH--, and the rings A and B are each independently unsubstituted or substituted by C₁ -C₄ -alkyl, hydroxyl, C₁ -C₄ -alkoxy, amino, C₁ -C₄ -monoalkyl, -dialkyl-amino, hydroxysulfonyl or A and B are each independently unsubstituted or substituted benzofused rings where said substituents are as defined above.
 2. An ink jet process as claimed in claim 1, wherein the dye is a dye of the formula I whereR¹ and R³ are each hydrogen, methyl or ethyl, R² and R⁴ are each hydrogen, dimethylaminopropyl or diethylaminopropyl and X is a bridge member of the formula IIa or IIIa where Y is C₂ -C₄ -alkylene, --CO--NH-- or --SO₂ NH--. 